The functional organization of the primate retina is investigated using techniques which identify single cells or single populations of neurons. With Golgi impregnation, electron microscopy (EM) Golgi-EM, formaldehyde-induced fluorescence (FIF) for catecholamines, and immunohistochemistry, the component elements of the neuronal circuitry are identified. By these studies of the structure, connectons, synapses, and neurotransmitters of Macaca retina, the functional role of neurons in the processing of the visual image in the retina can be defined. Bipolar cells, a class of retinal interneuron with dendrites in the outer plexiform layer that contact photoreceptors, and exons terminating in the inner plexiform layer convey the receptive field center responses of ganglion cells. Now another morphological type of bipolar cell has been found in Golgi preparations of the rhesus monkey retina, and it displays selective and patterned distribution of its dendritic contacts with blue-sensitive cone pedicles in the outer plaxiform layer. The discovery of the blue-cone bipolar cell and the subsequent identification of specific parts of the blue-sensitive retinal circuitry is a major advance in understanding the neuronal bases of color vision in the primate visual system.